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 <body class="h-entry">
  <div class="head">
   <p data-fill-with="logo"><a class="logo" href="https://www.w3.org/"> <img alt="W3C" height="48" src="https://www.w3.org/StyleSheets/TR/2016/logos/W3C" width="72"> </a> </p>
   <h1 class="p-name no-ref" id="title">CSS Transitions Level 2</h1>
   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Editor’s Draft, <time class="dt-updated" datetime="1970-01-01">1 January 1970</time></span></h2>
   <details>
    <summary>Specification Metadata</summary>
    <div data-fill-with="spec-metadata">
     <dl>
      <dt>This version:
      <dd><a class="u-url" href="https://drafts.csswg.org/css-transitions-2/">https://drafts.csswg.org/css-transitions-2/</a>
      <dt>Issue Tracking:
      <dd><a href="https://www.w3.org/Bugs/Public/buglist.cgi?query_format=advanced&amp;amp;product=CSS&amp;amp;component=Transitions&amp;amp;resolution=---">Bugzilla bugs for all levels</a>
      <dd><a href="https://github.com/w3c/csswg-drafts/labels/css-transitions-2-2">GitHub Issues</a>
      <dt class="editor">Editor:
      <dd class="editor p-author h-card vcard" data-editor-id="15393"><a class="p-name fn u-url url" href="https://dbaron.org/">L. David Baron</a> (<a class="p-org org" href="https://www.mozilla.org/">Mozilla</a>)
      <dt>Suggest an Edit for this Spec:
      <dd><a href="https://github.com/w3c/csswg-drafts/blob/master/css-transitions-2-2/Overview.bs">GitHub Editor</a>
     </dl>
    </div>
   </details>
   <div data-fill-with="warning"></div>
   <p class="copyright" data-fill-with="copyright"><a href="https://www.w3.org/Consortium/Legal/ipr-notice#Copyright">Copyright</a> © 1970 <a href="https://www.w3.org/"><abbr title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a href="https://www.csail.mit.edu/"><abbr title="Massachusetts Institute of Technology">MIT</abbr></a>, <a href="https://www.ercim.eu/"><abbr title="European Research Consortium for Informatics and Mathematics">ERCIM</abbr></a>, <a href="https://www.keio.ac.jp/">Keio</a>, <a href="https://ev.buaa.edu.cn/">Beihang</a>). W3C <a href="https://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>, <a href="https://www.w3.org/Consortium/Legal/ipr-notice#W3C_Trademarks">trademark</a> and <a href="https://www.w3.org/Consortium/Legal/2015/copyright-software-and-document">permissive document license</a> rules apply. </p>
   <hr title="Separator for header">
  </div>
  <div class="p-summary" data-fill-with="abstract">
   <h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
   <p>CSS Transitions allows property changes in CSS values to occur smoothly over a specified duration.</p>
    <a href="https://www.w3.org/TR/CSS/">CSS</a> is a language for describing the rendering of structured documents
(such as HTML and XML)
on screen, on paper, etc. 
  </div>
  <h2 class="no-num no-toc no-ref heading settled" id="status"><span class="content">Status of this document</span></h2>
  <div data-fill-with="status">
   <p> This is a public copy of the editors’ draft.
	It is provided for discussion only and may change at any moment.
	Its publication here does not imply endorsement of its contents by W3C.
	Don’t cite this document other than as work in progress. </p>
   <p> <a href="https://github.com/w3c/csswg-drafts/issues">GitHub Issues</a> are preferred for discussion of this specification.
	When filing an issue, please put the text “css-transitions-2” in the title,
	preferably like this:
	“[css-transitions-2] <i data-lt>…summary of comment…</i>”.
	All issues and comments are <a href="https://lists.w3.org/Archives/Public/public-css-archive/">archived</a>,
	and there is also a <a href="https://lists.w3.org/Archives/Public/www-style/">historical archive</a>. </p>
   <p> This document was produced by the <a href="https://www.w3.org/Style/CSS/">CSS Working Group</a>. </p>
   <p> This document was produced by a group operating under
	the <a href="https://www.w3.org/Consortium/Patent-Policy/">W3C Patent Policy</a>.
	W3C maintains a <a href="https://www.w3.org/2004/01/pp-impl/32061/status" rel="disclosure">public list of any patent disclosures</a> made in connection with the deliverables of the group;
	that page also includes instructions for disclosing a patent.
	An individual who has actual knowledge of a patent which the individual believes contains <a href="https://www.w3.org/Consortium/Patent-Policy/#def-essential">Essential Claim(s)</a> must disclose the information in accordance with <a href="https://www.w3.org/Consortium/Patent-Policy/#sec-Disclosure">section 6 of the W3C Patent Policy</a>. </p>
   <p> This document is governed by the <a href="https://www.w3.org/2019/Process-20190301/" id="w3c_process_revision">1 March 2019 W3C Process Document</a>. </p>
   <p></p>
  </div>
  <div data-fill-with="at-risk"></div>
  <nav data-fill-with="table-of-contents" id="toc">
   <h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
   <ol class="toc" role="directory">
    <li><a href="#delta"><span class="secno">1</span> <span class="content">Delta specification</span></a>
    <li>
     <a href="#starting"><span class="secno">2</span> <span class="content">Starting of transitions</span></a>
     <ol class="toc">
      <li><a href="#transition-property-name"><span class="secno">2.1</span> <span class="content">The transition property name</span></a>
      <li><a href="#transition-timing-function"><span class="secno">2.2</span> <span class="content">The transition timing function</span></a>
      <li><a href="#owning-element-section"><span class="secno">2.3</span> <span class="content">Owning element</span></a>
      <li><a href="#animation-composite-order"><span class="secno">2.4</span> <span class="content">Animation composite order</span></a>
     </ol>
    <li>
     <a href="#transition-events"><span class="secno">3</span> <span class="content">Transition Events</span></a>
     <ol class="toc">
      <li><a href="#event-dispatch"><span class="secno">3.1</span> <span class="content">Event dispatch</span></a>
     </ol>
    <li>
     <a href="#interface-dom"><span class="secno">4</span> <span class="content">DOM Interfaces</span></a>
     <ol class="toc">
      <li><a href="#the-CSSTransition-interface"><span class="secno">4.1</span> <span class="content">The CSSTransition interface</span></a>
      <li><a href="#requirements-on-pending-style-changes"><span class="secno">4.2</span> <span class="content">Requirements on pending style changes</span></a>
     </ol>
    <li><a href="#issues-common"><span class="secno">5</span> <span class="content">Issues commonly raised as issues with previous levels</span></a>
    <li><a href="#issues-spec"><span class="secno">6</span> <span class="content">Issues deferred from previous levels of the spec</span></a>
    <li>
     <a href="#conformance"><span class="secno"></span> <span class="content"> Conformance</span></a>
     <ol class="toc">
      <li><a href="#document-conventions"><span class="secno"></span> <span class="content"> Document conventions</span></a>
      <li><a href="#conform-classes"><span class="secno"></span> <span class="content"> Conformance classes</span></a>
      <li>
       <a href="#conform-responsible"><span class="secno"></span> <span class="content"> Requirements for Responsible Implementation of CSS</span></a>
       <ol class="toc">
        <li><a href="#conform-partial"><span class="secno"></span> <span class="content"> Partial Implementations</span></a>
        <li><a href="#conform-future-proofing"><span class="secno"></span> <span class="content"> Implementations of Unstable and Proprietary Features</span></a>
        <li><a href="#conform-testing"><span class="secno"></span> <span class="content"> Implementations of CR-level Features</span></a>
       </ol>
     </ol>
    <li>
     <a href="#index"><span class="secno"></span> <span class="content">Index</span></a>
     <ol class="toc">
      <li><a href="#index-defined-here"><span class="secno"></span> <span class="content">Terms defined by this specification</span></a>
      <li><a href="#index-defined-elsewhere"><span class="secno"></span> <span class="content">Terms defined by reference</span></a>
     </ol>
    <li>
     <a href="#references"><span class="secno"></span> <span class="content">References</span></a>
     <ol class="toc">
      <li><a href="#normative"><span class="secno"></span> <span class="content">Normative References</span></a>
      <li><a href="#informative"><span class="secno"></span> <span class="content">Informative References</span></a>
     </ol>
    <li><a href="#idl-index"><span class="secno"></span> <span class="content">IDL Index</span></a>
    <li><a href="#issues-index"><span class="secno"></span> <span class="content">Issues Index</span></a>
   </ol>
  </nav>
  <main>
   <h2 class="heading settled" data-level="1" id="delta"><span class="secno">1. </span><span class="content">Delta specification</span><a class="self-link" href="#delta"></a></h2>
   <p>This is a delta specification, meaning that it currently contains
	only the differences from CSS Transitions Level 1 <a data-link-type="biblio" href="#biblio-css3-transitions">[CSS3-TRANSITIONS]</a>.
	Once the Level 1 specification is closer to complete, it will be merged
	with the additions here into a complete level 2 specification.</p>
   <h2 class="heading settled" data-level="2" id="starting"><span class="secno">2. </span><span class="content">Starting of transitions</span><a class="self-link" href="#starting"></a></h2>
   <p>Associated with each top-level browsing context is a <dfn class="dfn-paneled" data-dfn-type="dfn" data-lt="current transition generation" data-noexport id="current-transition-generation">current transition
generation</dfn> that is incremented on each <a data-link-type="dfn" href="https://drafts.csswg.org/css-transitions-1/#style-change-event" id="ref-for-style-change-event">style change event</a>.</p>
   <p>Each time a new transition is generated, the current value of the (already
incremented) <a data-link-type="dfn" href="#current-transition-generation" id="ref-for-current-transition-generation">current transition generation</a> is stored as the
transition’s <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="transition-generation">transition generation</dfn>.</p>
   <h3 class="heading settled" data-level="2.1" id="transition-property-name"><span class="secno">2.1. </span><span class="content">The transition property name</span><a class="self-link" href="#transition-property-name"></a></h3>
   <p>Although the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-transitions-1/#propdef-transition-property" id="ref-for-propdef-transition-property">transition-property</a> may specify shorthand properties and the <a class="css" data-link-type="maybe" href="https://drafts.csswg.org/css-transitions-1/#valdef-transition-property-all" id="ref-for-valdef-transition-property-all">all</a> keyword, individual transitions are generated for each longhand
sub-property that is animatable. The <dfn class="dfn-paneled" data-dfn-type="dfn" data-lt="expanded transition property name" data-noexport id="expanded-transition-property-name">expanded transition property
name</dfn> of a transition is the name of the longhand sub-property for which
the transition was generated (e.g. <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-backgrounds-3/#propdef-border-left-width" id="ref-for-propdef-border-left-width">border-left-width</a>).</p>
   <h3 class="heading settled" data-level="2.2" id="transition-timing-function"><span class="secno">2.2. </span><span class="content">The transition timing function</span><a class="self-link" href="#transition-timing-function"></a></h3>
   <p>When creating a <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/web-animations-1/#keyframeeffect" id="ref-for-keyframeeffect">KeyframeEffect</a></code> for a transition, the effect’s <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/web-animations-1/#dom-effecttiming-easing" id="ref-for-dom-effecttiming-easing">easing</a></code> option is set to the value of the matching <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-transitions-1/#propdef-transition-timing-function" id="ref-for-propdef-transition-timing-function">transition-timing-function</a> property,
which must be used by <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/web-animations-1/#dom-animationeffect-getcomputedtiming" id="ref-for-dom-animationeffect-getcomputedtiming">getComputedTiming()</a></code>.</p>
   <p class="note" role="note"><span>Note:</span> Unlike CSS animations, the timing function for CSS transitions applies to
the animation effect as opposed to the individual keyframes since this allows
it to be reflected in the <a data-link-type="dfn">transformed progress</a> as used when calculating
the reversing shortening factor.</p>
   <h3 class="heading settled" data-level="2.3" id="owning-element-section"><span class="secno">2.3. </span><span class="content">Owning element</span><a class="self-link" href="#owning-element-section"></a></h3>
   <p>The <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="owning-element">owning element</dfn> of a transition refers to the element or
pseudo-element to which the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-transitions-1/#propdef-transition-property" id="ref-for-propdef-transition-property①">transition-property</a> property was applied that
generated the animation.</p>
   <p>If a transition was generated directly by script (e.g. using the <code class="idl"><a data-link-type="idl" href="#csstransition" id="ref-for-csstransition">CSSTransition</a></code> constructor) then it has no <a data-link-type="dfn" href="#owning-element" id="ref-for-owning-element">owning element</a>.</p>
   <p>If a transition generated using the markup defined in this specification is
later disassociated from that markup because it is cancelled or replaced by
a newer transition, the animation is disassociated from its <a data-link-type="dfn" href="#owning-element" id="ref-for-owning-element①">owning
element</a> (that is, it has no <span id="ref-for-owning-element②">owning element</span> from that point
forwards).</p>
   <p class="issue" id="issue-e8892835"><a class="self-link" href="#issue-e8892835"></a> Define the above more precisely once we rewrite firing of transitions
in terms of Web Animations concepts (specifically when we spell out when we
cancel an animation).</p>
   <h3 class="heading settled" data-level="2.4" id="animation-composite-order"><span class="secno">2.4. </span><span class="content">Animation composite order</span><a class="self-link" href="#animation-composite-order"></a></h3>
   <p><a data-link-type="dfn" href="https://w3c.github.io/web-animations/#animation" id="ref-for-animation">Animations</a> generated from the markup and
interfaces (e.g. the <code class="idl"><a data-link-type="idl" href="#csstransition" id="ref-for-csstransition①">CSSTransition</a></code> constructor) defined in this
specification have an <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#animation-class" id="ref-for-animation-class">animation class</a> of ‘CSS Transition’.</p>
   <p>CSS Transitions have an <em>earlier</em> composite order that CSS Animations
and animations without a specific <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#animation-class" id="ref-for-animation-class①">animation class</a>.</p>
   <p>Within the set of CSS Transitions, two animations <var>A</var> and <var>B</var> are sorted in composite order (first to last) as follows:</p>
   <ol>
    <li data-md>
     <p>If neither <var>A</var> nor <var>B</var> has an <a data-link-type="dfn" href="#owning-element" id="ref-for-owning-element③">owning element</a>,
sort based on their relative position in the <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#global-animation-list" id="ref-for-global-animation-list">global animation list</a>.</p>
    <li data-md>
     <p>Otherwise, if  only one of <var>A</var> or <var>B</var> has an <a data-link-type="dfn" href="#owning-element" id="ref-for-owning-element④">owning
element</a>, let the animation <em>with</em> an <span id="ref-for-owning-element⑤">owning element</span> sort
first.</p>
    <li data-md>
     <p>Otherwise, if the <a data-link-type="dfn" href="#owning-element" id="ref-for-owning-element⑥">owning element</a> of <var>A</var> and <var>B</var> differs, sort <var>A</var> and <var>B</var> by <a data-link-type="dfn" href="https://dom.spec.whatwg.org/#concept-tree-order" id="ref-for-concept-tree-order">tree order</a> of their corresponding <span id="ref-for-owning-element⑦">owning elements</span>.
With regard to pseudo-elements, the sort order is as follows:</p>
     <ul>
      <li data-md>
       <p>element</p>
      <li data-md>
       <p>::marker</p>
      <li data-md>
       <p>::before</p>
      <li data-md>
       <p>::after</p>
      <li data-md>
       <p>element children</p>
     </ul>
    <li data-md>
     <p>Otherwise, if <var>A</var> and <var>B</var> have different <a data-link-type="dfn" href="#transition-generation" id="ref-for-transition-generation">transition
generation</a> values, sort by their corresponding <span id="ref-for-transition-generation①">transition generation</span> in ascending order.</p>
    <li data-md>
     <p>Otherwise, sort <var>A</var> and <var>B</var> in ascending order by the
Unicode codepoints that make up the <a data-link-type="dfn" href="#expanded-transition-property-name" id="ref-for-expanded-transition-property-name">expanded transition property
name</a> of each transition (i.e. without attempting case conversion and
such that ‘-moz-column-width’ sorts before
‘column-width’).</p>
   </ol>
   <p>Transitions generated using the markup defined in this specification are <em>not</em> added to the <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#global-animation-list" id="ref-for-global-animation-list①">global animation list</a> when they are created.
Instead, these animations are appended to the <span id="ref-for-global-animation-list②">global animation list</span> at
the first moment when they transition out of the <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#idle-play-state" id="ref-for-idle-play-state">idle play state</a> after
being disassociated from their <a data-link-type="dfn" href="#owning-element" id="ref-for-owning-element⑧">owning element</a>.
Transitions that have been disassociated from their <span id="ref-for-owning-element⑨">owning element</span> but are still <span id="ref-for-idle-play-state①">idle</span> do not have a defined
composite order.</p>
   <p class="note" role="note"><span>Note,</span> this behavior relies on the fact that disassociating a transition
from its <a data-link-type="dfn" href="#owning-element" id="ref-for-owning-element①⓪">owning element</a> always causes it to enter (or remain) in the <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#idle-play-state" id="ref-for-idle-play-state②">idle play state</a>.</p>
   <p>Transitions created using the <code class="idl"><a data-link-type="idl" href="#csstransition" id="ref-for-csstransition②">CSSTransition</a></code> constructor are appended
to the <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#global-animation-list" id="ref-for-global-animation-list③">global animation list</a> at the moment they are constructed.</p>
   <h2 class="heading settled" data-level="3" id="transition-events"><span class="secno">3. </span><span class="content">Transition Events</span><a class="self-link" href="#transition-events"></a></h2>
   <h3 class="heading settled" data-level="3.1" id="event-dispatch"><span class="secno">3.1. </span><span class="content">Event dispatch</span><a class="self-link" href="#event-dispatch"></a></h3>
   <p class="note" role="note"><span>Note,</span> this is a more general description of event dispatch than that of CSS
Transitions Level 1 <a data-link-type="biblio" href="#biblio-css3-transitions">[CSS3-TRANSITIONS]</a> since it must account for the
possibility of animations being seeked or reversed using the Web Animations API <a data-link-type="biblio" href="#biblio-web-animations">[WEB-ANIMATIONS]</a>. Furthermore, it is possible using the Web Animations API
to substitute the transition effect with an entirely different effect with
properties not normally used with transitions (e.g. an effect that repeats
multiple times) and hence this section provides a generic definition that
accounts for the full complexity of the Web Animations model.</p>
   <p>To avoid firing redundant events, the set of events to dispatch is based
on comparing the <a data-link-type="dfn" href="#transition-phase" id="ref-for-transition-phase">phase</a> of the transition in the
previous <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#sampling" id="ref-for-sampling">sample</a> (animation frame) to its current state.</p>
   <p>The <dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="transition-phase">transition phase</dfn> of a transition is initially ‘idle’
and is updated on each sample according to the first matching condition from
below:</p>
   <dl class="switch">
    <dt>If the transition has no <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#target-effect" id="ref-for-target-effect">target effect</a>, 
    <dd>
      The transition phase is set according to the first matching condition
     from below: 
     <dl class="switch">
      <dt>If the transition has an <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#unresolved" id="ref-for-unresolved">unresolved</a> <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#current-time" id="ref-for-current-time">current time</a>, 
      <dd>The transition phase is ‘idle’. 
      <dt>If the transition has a <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#current-time" id="ref-for-current-time①">current time</a> &lt; 0, 
      <dd>The transition phase is ‘before’. 
      <dt>Otherwise, 
      <dd>The transition phase is ‘after’. 
     </dl>
    <dt>If the transition is <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#pending-play-state" id="ref-for-pending-play-state">pending</a> and its
       phase was previously ‘idle’ or ‘pending’, 
    <dd>The transition phase is ‘pending’. 
    <dt>Otherwise, 
    <dd>The transition phase is the <a href="https://www.w3.org/TR/web-animations-1/#animation-effect-phases-and-states">phase</a> of its <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#target-effect" id="ref-for-target-effect①">target effect</a>. 
   </dl>
   <p>For calculating the <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#Events-TransitionEvent-elapsedTime" id="ref-for-Events-TransitionEvent-elapsedTime">elapsedTime</a></code> of each event, the following
definitions are used:</p>
   <ul>
    <li data-md>
     <p><dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="interval-start">interval start</dfn> = <code>max(min(-<a data-link-type="dfn" href="https://w3c.github.io/web-animations/#start-delay" id="ref-for-start-delay">start delay</a>, <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#active-duration" id="ref-for-active-duration">active duration</a>), 0)</code></p>
    <li data-md>
     <p><dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="interval-end">interval end</dfn> = <code>max(min(<a data-link-type="dfn" href="https://w3c.github.io/web-animations/#target-effect-end" id="ref-for-target-effect-end">target effect end</a> - <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#start-delay" id="ref-for-start-delay①">start delay</a>, <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#active-duration" id="ref-for-active-duration①">active duration</a>), 0)</code></p>
   </ul>
   <p>In the above formulae, references to the <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#start-delay" id="ref-for-start-delay②">start delay</a>, <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#active-duration" id="ref-for-active-duration②">active
duration</a>, <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#current-iteration" id="ref-for-current-iteration">current iteration</a>, <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#iteration-start" id="ref-for-iteration-start">iteration start</a>, and <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#iteration-duration" id="ref-for-iteration-duration">iteration duration</a> of a transition should be understood to refer
to the corresponding properties of the transition’s <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#target-effect" id="ref-for-target-effect②">target effect</a>.</p>
   <p>Each time an animation is <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#sampling" id="ref-for-sampling①">sampled</a>, the events to
dispatch are determined by comparing the <a data-link-type="dfn" href="#transition-phase" id="ref-for-transition-phase①">transition phase</a> before and
after the sample as follows:</p>
   <table class="event-state-transitions">
    <thead>
     <tr>
      <th>Change
      <th>Events dispatched
      <th><dfn class="dfn-paneled" data-dfn-type="dfn" data-noexport id="elapsed-time">Elapsed time</dfn> (ms)
    <tbody>
     <tr>
      <td>idle → pending or before
      <td><code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionrun" id="ref-for-transitionrun">transitionrun</a></code>
      <td><a data-link-type="dfn" href="#interval-start" id="ref-for-interval-start">interval start</a>
     <tr>
      <td rowspan="2">idle → active <a href="#multiple-events-note">٭</a>
      <td><code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionrun" id="ref-for-transitionrun①">transitionrun</a></code>
      <td rowspan="2"><a data-link-type="dfn" href="#interval-start" id="ref-for-interval-start①">interval start</a>
     <tr>
      <td><code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionstart" id="ref-for-transitionstart">transitionstart</a></code>
     <tr>
      <td rowspan="3">idle → after <a href="#multiple-events-note">٭</a>
      <td><code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionrun" id="ref-for-transitionrun②">transitionrun</a></code>
      <td rowspan="2"><a data-link-type="dfn" href="#interval-start" id="ref-for-interval-start②">interval start</a>
     <tr>
      <td><code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionstart" id="ref-for-transitionstart①">transitionstart</a></code>
     <tr>
      <td><code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionend" id="ref-for-transitionend">transitionend</a></code>
      <td><a data-link-type="dfn" href="#interval-end" id="ref-for-interval-end">interval end</a>
     <tr>
      <td>pending or before → active
      <td><code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionstart" id="ref-for-transitionstart②">transitionstart</a></code>
      <td><a data-link-type="dfn" href="#interval-start" id="ref-for-interval-start③">interval start</a>
     <tr>
      <td rowspan="2">pending or before → after <a href="#multiple-events-note">٭</a>
      <td><code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionstart" id="ref-for-transitionstart③">transitionstart</a></code>
      <td><a data-link-type="dfn" href="#interval-start" id="ref-for-interval-start④">interval start</a>
     <tr>
      <td><code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionend" id="ref-for-transitionend①">transitionend</a></code>
      <td><a data-link-type="dfn" href="#interval-end" id="ref-for-interval-end①">interval end</a>
     <tr>
      <td>active → after
      <td><code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionend" id="ref-for-transitionend②">transitionend</a></code>
      <td><a data-link-type="dfn" href="#interval-end" id="ref-for-interval-end②">interval end</a>
     <tr>
      <td>active → before
      <td><code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionend" id="ref-for-transitionend③">transitionend</a></code>
      <td><a data-link-type="dfn" href="#interval-start" id="ref-for-interval-start⑤">interval start</a>
     <tr>
      <td>after → active
      <td><code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionstart" id="ref-for-transitionstart④">transitionstart</a></code>
      <td><a data-link-type="dfn" href="#interval-end" id="ref-for-interval-end③">interval end</a>
     <tr>
      <td rowspan="2">after → before <a href="#multiple-events-note">٭</a>
      <td><code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionstart" id="ref-for-transitionstart⑤">transitionstart</a></code>
      <td><a data-link-type="dfn" href="#interval-end" id="ref-for-interval-end④">interval end</a>
     <tr>
      <td><code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionend" id="ref-for-transitionend④">transitionend</a></code>
      <td><a data-link-type="dfn" href="#interval-start" id="ref-for-interval-start⑥">interval start</a>
     <tr>
      <td><em>not</em> idle and <em>not</em> after → idle
      <td><code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitioncancel" id="ref-for-transitioncancel">transitioncancel</a></code>
      <td>The <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#active-time" id="ref-for-active-time">active time</a> of the animation at the moment it was cancelled
          calculated using a <a data-link-type="dfn" href="https://w3c.github.io/web-animations/#fill-mode" id="ref-for-fill-mode">fill mode</a> of both.
   </table>
   <p id="multiple-events-note">٭ Where multiple events are listed for
a state change, all events are dispatched in the order listed and in immediate
succession.</p>
   <p>Since the <a data-link-type="dfn" href="#elapsed-time" id="ref-for-elapsed-time">elapsed time</a> defined in the table and procedure above is
expressed in milliseconds, it must be divided by 1,000 to produce a value in
seconds before being assigned to the <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#Events-TransitionEvent-elapsedTime" id="ref-for-Events-TransitionEvent-elapsedTime①">elapsedTime</a></code> member of
the <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionevent" id="ref-for-transitionevent">TransitionEvent</a></code>.</p>
   <div class="note" role="note">
    <p>The above state transition chart ensures that, with the exception of
  transitions that are paused or have an infinite running time, the following
  invariants hold:</p>
    <ul>
     <li data-md>
      <p>For every <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionrun" id="ref-for-transitionrun③">transitionrun</a></code> event there will be a exactly one <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionend" id="ref-for-transitionend⑤">transitionend</a></code> <em>or</em> <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitioncancel" id="ref-for-transitioncancel①">transitioncancel</a></code> and never both.</p>
     <li data-md>
      <p>For every <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionstart" id="ref-for-transitionstart⑥">transitionstart</a></code> event there will be a exactly one <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionend" id="ref-for-transitionend⑥">transitionend</a></code> <em>or</em> <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitioncancel" id="ref-for-transitioncancel②">transitioncancel</a></code> and never both.</p>
     <li data-md>
      <p>Every <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionend" id="ref-for-transitionend⑦">transitionend</a></code> event is preceded by a corresponding <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionstart" id="ref-for-transitionstart⑦">transitionstart</a></code> event.</p>
    </ul>
    <p>The typical sequences of events, then, are as follows:</p>
    <ul>
     <li data-md>
      <p>Regular playback: <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionrun" id="ref-for-transitionrun④">transitionrun</a></code>, <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionstart" id="ref-for-transitionstart⑧">transitionstart</a></code>, <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionend" id="ref-for-transitionend⑧">transitionend</a></code>.</p>
     <li data-md>
      <p>Interrupted playback: <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionrun" id="ref-for-transitionrun⑤">transitionrun</a></code>, <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionstart" id="ref-for-transitionstart⑨">transitionstart</a></code>, <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitioncancel" id="ref-for-transitioncancel③">transitioncancel</a></code>.</p>
     <li data-md>
      <p>Interrupted playback during delay or pending phase: <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionrun" id="ref-for-transitionrun⑥">transitionrun</a></code>, <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitioncancel" id="ref-for-transitioncancel④">transitioncancel</a></code>.</p>
     <li data-md>
      <p>Reversed playback after completion: <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionrun" id="ref-for-transitionrun⑦">transitionrun</a></code>, <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionstart" id="ref-for-transitionstart①⓪">transitionstart</a></code>, <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionend" id="ref-for-transitionend⑨">transitionend</a></code>, <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionstart" id="ref-for-transitionstart①①">transitionstart</a></code>, <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/css-transitions-1/#transitionend" id="ref-for-transitionend①⓪">transitionend</a></code>.</p>
    </ul>
   </div>
   <h2 class="heading settled" data-level="4" id="interface-dom"><span class="secno">4. </span><span class="content">DOM Interfaces</span><a class="self-link" href="#interface-dom"></a></h2>
   <h3 class="heading settled" data-level="4.1" id="the-CSSTransition-interface"><span class="secno">4.1. </span><span class="content">The CSSTransition interface</span><a class="self-link" href="#the-CSSTransition-interface"></a></h3>
<pre class="idl highlight def">[<a class="idl-code" data-link-type="extended-attribute" href="https://heycam.github.io/webidl/#Exposed" id="ref-for-Exposed"><c- g>Exposed</c-></a>=<c- n>Window</c->]
<c- b>interface</c-> <dfn class="dfn-paneled idl-code" data-dfn-type="interface" data-export id="csstransition"><code><c- g>CSSTransition</c-></code></dfn> : <a class="n" data-link-type="idl-name" href="https://w3c.github.io/web-animations/#animation" id="ref-for-animation①"><c- n>Animation</c-></a> {
  <c- b>readonly</c-> <c- b>attribute</c-> <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/cssom-1/#cssomstring" id="ref-for-cssomstring"><c- n>CSSOMString</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="CSSOMString" href="#dom-csstransition-transitionproperty" id="ref-for-dom-csstransition-transitionproperty"><c- g>transitionProperty</c-></a>;
};
</pre>
   <dl>
    <dt data-md><dfn class="dfn-paneled idl-code" data-dfn-for="CSSTransition" data-dfn-type="attribute" data-export id="dom-csstransition-transitionproperty"><code>transitionProperty</code></dfn>, <span> of type <a data-link-type="idl-name" href="https://drafts.csswg.org/cssom-1/#cssomstring" id="ref-for-cssomstring①">CSSOMString</a>, readonly</span>
    <dd data-md>
     <p>The <a data-link-type="dfn" href="#expanded-transition-property-name" id="ref-for-expanded-transition-property-name①">expanded transition property name</a> of this transition.</p>
   </dl>
   <div class="issue" id="issue-25ee9f1c">
    <a class="self-link" href="#issue-25ee9f1c"></a> 
    <p>This interface needs a constructor. Perhaps something like the following,</p>
<pre class="idl highlight def">[<dfn class="idl-code" data-dfn-for="CSSTransition" data-dfn-type="constructor" data-export data-lt="CSSTransition(target, transitionProperty, transitionValue, options)|CSSTransition(target, transitionProperty, transitionValue)" id="dom-csstransition-csstransition"><code><c- g>Constructor</c-></code><a class="self-link" href="#dom-csstransition-csstransition"></a></dfn> (<a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/web-animations-1/#animatable" id="ref-for-animatable"><c- n>Animatable</c-></a>? <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options)" data-dfn-type="argument" data-export id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-target"><code><c- g>target</c-></code><a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-target"></a></dfn>,
              <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/cssom-1/#cssomstring" id="ref-for-cssomstring②"><c- n>CSSOMString</c-></a> <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options)" data-dfn-type="argument" data-export id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-transitionproperty"><code><c- g>transitionProperty</c-></code><a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-transitionproperty"></a></dfn>,
              <c- b>any</c-> <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options)" data-dfn-type="argument" data-export id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-transitionvalue"><code><c- g>transitionValue</c-></code><a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-transitionvalue"></a></dfn>,
              <c- b>optional</c-> (<a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-unrestricted-double" id="ref-for-idl-unrestricted-double"><c- b>unrestricted</c-> <c- b>double</c-></a> <c- b>or</c-> <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/web-animations-1/#dictdef-keyframeeffectoptions" id="ref-for-dictdef-keyframeeffectoptions"><c- n>KeyframeEffectOptions</c-></a>) <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options)" data-dfn-type="argument" data-export id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-options"><code><c- g>options</c-></code><a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-options"></a></dfn>),
 <dfn class="idl-code" data-dfn-for="CSSTransition" data-dfn-type="constructor" data-export data-lt="CSSTransition(target, transitionProperty, transitionValue, options, timeline)" id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline"><code><c- g>Constructor</c-></code><a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline"></a></dfn> (<a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/web-animations-1/#animatable" id="ref-for-animatable①"><c- n>Animatable</c-></a>? <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options, timeline)" data-dfn-type="argument" data-export id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-target"><code><c- g>target</c-></code><a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-target"></a></dfn>,
              <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/cssom-1/#cssomstring" id="ref-for-cssomstring③"><c- n>CSSOMString</c-></a> <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options, timeline)" data-dfn-type="argument" data-export id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-transitionproperty"><code><c- g>transitionProperty</c-></code><a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-transitionproperty"></a></dfn>,
              <c- b>any</c-> <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options, timeline)" data-dfn-type="argument" data-export id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-transitionvalue"><code><c- g>transitionValue</c-></code><a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-transitionvalue"></a></dfn>,
              (<a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-unrestricted-double" id="ref-for-idl-unrestricted-double①"><c- b>unrestricted</c-> <c- b>double</c-></a> <c- b>or</c-> <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/web-animations-1/#dictdef-keyframeeffectoptions" id="ref-for-dictdef-keyframeeffectoptions①"><c- n>KeyframeEffectOptions</c-></a>) <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options, timeline)" data-dfn-type="argument" data-export id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-options"><code><c- g>options</c-></code><a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-options"></a></dfn>,
              <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/web-animations-1/#animationtimeline" id="ref-for-animationtimeline"><c- n>AnimationTimeline</c-></a>? <dfn class="idl-code" data-dfn-for="CSSTransition/CSSTransition(target, transitionProperty, transitionValue, options, timeline)" data-dfn-type="argument" data-export id="dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-timeline"><code><c- g>timeline</c-></code><a class="self-link" href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-timeline"></a></dfn>)]
<c- b>partial</c-> <c- b>interface</c-> <a class="idl-code" data-link-type="interface" href="#csstransition" id="ref-for-csstransition③"><c- g>CSSTransition</c-></a> { };
</pre>
    <p>Using <code>any</code> as the type for <code>transitionValue</code> would allow
the following usage:</p>
<pre class="example lang-javascript highlight" id="example-c11a4c13"><a class="self-link" href="#example-c11a4c13"></a><c- a>var</c-> transition <c- o>=</c-> <c- k>new</c-> CSSTransition<c- p>(</c->elem<c- p>,</c-> <c- t>'opacity'</c-><c- p>,</c-> <c- mi>1</c-><c- p>,</c-> <c- mi>2000</c-><c- p>);</c->
transition<c- p>.</c->play<c- p>();</c->
</pre>
    <p>The above example, however, is <em>not</em> equivalent to triggering a
transition. It has the following differences:</p>
    <ul>
     <li data-md>
      <p>It does not update the specified style.</p>
     <li data-md>
      <p>It would not cancel any existing transition on the given property unless
we add special wording to that effect.</p>
     <li data-md>
      <p>It would exhibit different composite order to a regular transition
(this should be easily fixed, however).</p>
     <li data-md>
      <p>It has been suggested that <a href="https://github.com/w3c/web-animations/issues/62#issuecomment-117357703">script-generated
animations should not apply to the transition level of the cascade</a>.</p>
    </ul>
    <p>It is unclear how much we should extend the <code class="idl"><a data-link-type="idl" href="#csstransition" id="ref-for-csstransition④">CSSTransition</a></code> constructor to
overcome the above limitations so that it can be used to generate transitions
programmatically, or whether we should introduce a separate helper method such
as has been <a href="https://lists.w3.org/Archives/Public/www-style/2011Mar/0729.html">suggested
elsewhere</a>.</p>
   </div>
   <h3 class="heading settled" data-level="4.2" id="requirements-on-pending-style-changes"><span class="secno">4.2. </span><span class="content">Requirements on pending style changes</span><a class="self-link" href="#requirements-on-pending-style-changes"></a></h3>
   <p>Various operations may affect the <a data-link-type="dfn" href="https://drafts.csswg.org/css-cascade-4/#computed-value" id="ref-for-computed-value">computed values</a> of
properties on elements. User agents may, as an optimization, defer recomputing
these values until it becomes necessary.
However, all operations included in programming interface defined in this
specification, as well as those operations defined in Web Animations <a data-link-type="biblio" href="#biblio-web-animations">[WEB-ANIMATIONS]</a> that may return objects defined by this specification,
must produce a result consistent with having fully processed any such pending
changes to computed values.</p>
   <div class="note" role="note">
     As an example, in the following code fragment, when the specified value of <code>elem</code>’s <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-color-4/#propdef-opacity" id="ref-for-propdef-opacity">opacity</a> property is updated, a user agent may defer
recalculating the computed value of the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-animations-1/#propdef-animation" id="ref-for-propdef-animation">animation</a> property. 
    <p>The first time this occurs, calling <code class="idl"><a data-link-type="idl" href="https://drafts.csswg.org/cssom-1/#dom-window-getcomputedstyle" id="ref-for-dom-window-getcomputedstyle">getComputedStyle(elt)</a></code> and
subsequently accessing the <code>opacity</code> property of the result will
cause the user agent to recompute the value of opacity.</p>
    <p>After the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-color-4/#propdef-opacity" id="ref-for-propdef-opacity①">opacity</a> property is updated a second time, the <code class="idl"><a data-link-type="idl" href="https://www.w3.org/TR/web-animations-1/#dom-animatable-getanimations" id="ref-for-dom-animatable-getanimations">getAnimations()</a></code> method is called on <code>elem</code>.
This method is specified by Web Animations and can return <code class="idl"><a data-link-type="idl" href="#csstransition" id="ref-for-csstransition⑤">CSSTransition</a></code> objects as defined in this specification.
Hence, as result of the requirements in this section, the user agent must apply
any pending style changes thus generating a new <code class="idl"><a data-link-type="idl" href="#csstransition" id="ref-for-csstransition⑥">CSSTransition</a></code> for the <span class="property" id="ref-for-propdef-opacity②">opacity</span> property before returning its result.</p>
    <div>
<pre class="example lang-javascript highlight" id="example-9fcbce42"><a class="self-link" href="#example-9fcbce42"></a>elem<c- p>.</c->style<c- p>.</c->transition <c- o>=</c-> <c- t>'opacity 100s'</c-><c- p>;</c->
elem<c- p>.</c->style<c- p>.</c->opacity <c- o>=</c-> <c- t>'0'</c-><c- p>;</c->
window<c- p>.</c->getComputedStyle<c- p>(</c->elem<c- p>).</c->opacity<c- p>;</c-> <c- c1>// 0</c->
elem<c- p>.</c->style<c- p>.</c->opacity <c- o>=</c-> <c- t>'1'</c-><c- p>;</c->
elem<c- p>.</c->getAnimations<c- p>()[</c-><c- mi>0</c-><c- p>].</c->transitionProperty <c- c1>// 'opacity'</c->
</pre>
    </div>
   </div>
   <h2 class="heading settled" data-level="5" id="issues-common"><span class="secno">5. </span><span class="content">Issues commonly raised as issues with previous levels</span><a class="self-link" href="#issues-common"></a></h2>
   <p> These issues were commonly reported issues
		with the previous level of the specification. </p>
   <div class="issue" id="issue-af4a1d54">
    <a class="self-link" href="#issue-af4a1d54"></a> 
    <p> More powerful timing function syntax
			is a common request from developers.
			See, for example: <a href="https://lists.w3.org/Archives/Public/www-style/2013Jun/0376.html">2013 message</a> or <a href="https://lists.w3.org/Archives/Public/public-fx/2015JulSep/thread.html#msg34">2015 thread</a>. </p>
   </div>
   <div class="issue" id="issue-b197fc50">
    <a class="self-link" href="#issue-b197fc50"></a> 
    <p> Developers frequently have to trigger style flushes
			in order to force transitions to start.
			It would be good to have an API
			that would avoid this requirement.
			See, for example, <a href="https://lists.w3.org/Archives/Public/www-style/2011Mar/0729.html">2011 proposal</a>. </p>
   </div>
   <h2 class="heading settled" data-level="6" id="issues-spec"><span class="secno">6. </span><span class="content">Issues deferred from previous levels of the spec</span><a class="self-link" href="#issues-spec"></a></h2>
   <p> These issues were in previous levels of the specification,
		but may not turn out to be important in this level either. </p>
   <div class="issue" id="issue-5a3a5638"><a class="self-link" href="#issue-5a3a5638"></a> We may ultimately want to support a keypath syntax
		for the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-transitions-1/#propdef-transition-property" id="ref-for-propdef-transition-property②">transition-property</a> property.
		A keypath syntax
		would enable different transitions
		to be specified
		for components of a property.
		For example
		the blur of a shadow
		could have
		a different transition
		than the color of a shadow. </div>
  </main>
  <h2 class="no-ref no-num heading settled" id="conformance"><span class="content"> Conformance</span><a class="self-link" href="#conformance"></a></h2>
  <h3 class="heading settled" id="document-conventions"><span class="content"> Document conventions</span><a class="self-link" href="#document-conventions"></a></h3>
  <p>Conformance requirements are expressed with a combination of
	descriptive assertions and RFC 2119 terminology. The key words “MUST”,
	“MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”,
	“RECOMMENDED”, “MAY”, and “OPTIONAL” in the normative parts of this
	document are to be interpreted as described in RFC 2119.
	However, for readability, these words do not appear in all uppercase
	letters in this specification. </p>
  <p>All of the text of this specification is normative except sections
	explicitly marked as non-normative, examples, and notes. <a data-link-type="biblio" href="#biblio-rfc2119">[RFC2119]</a> </p>
  <p>Examples in this specification are introduced with the words “for example”
	or are set apart from the normative text with <code>class="example"</code>,
	like this: </p>
  <div class="example" id="example-ae2b6bc0">
   <a class="self-link" href="#example-ae2b6bc0"></a> 
   <p>This is an example of an informative example. </p>
  </div>
  <p>Informative notes begin with the word “Note” and are set apart from the
	normative text with <code>class="note"</code>, like this: </p>
  <p class="note" role="note">Note, this is an informative note. </p>
  <p>Advisements are normative sections styled to evoke special attention and are
	set apart from other normative text with <code>&lt;strong class="advisement"></code>, like
	this: <strong class="advisement"> UAs MUST provide an accessible alternative. </strong> </p>
  <h3 class="heading settled" id="conform-classes"><span class="content"> Conformance classes</span><a class="self-link" href="#conform-classes"></a></h3>
  <p>Conformance to this specification
	is defined for three conformance classes: </p>
  <dl>
   <dt>style sheet 
   <dd>A <a href="http://www.w3.org/TR/CSS2/conform.html#style-sheet">CSS
			style sheet</a>. 
   <dt>renderer 
   <dd>A <a href="http://www.w3.org/TR/CSS2/conform.html#user-agent">UA</a> that interprets the semantics of a style sheet and renders
			documents that use them. 
   <dt>authoring tool 
   <dd>A <a href="http://www.w3.org/TR/CSS2/conform.html#user-agent">UA</a> that writes a style sheet. 
  </dl>
  <p>A style sheet is conformant to this specification
	if all of its statements that use syntax defined in this module are valid
	according to the generic CSS grammar and the individual grammars of each
	feature defined in this module. </p>
  <p>A renderer is conformant to this specification
	if, in addition to interpreting the style sheet as defined by the
	appropriate specifications, it supports all the features defined
	by this specification by parsing them correctly
	and rendering the document accordingly. However, the inability of a
	UA to correctly render a document due to limitations of the device
	does not make the UA non-conformant. (For example, a UA is not
	required to render color on a monochrome monitor.) </p>
  <p>An authoring tool is conformant to this specification
	if it writes style sheets that are syntactically correct according to the
	generic CSS grammar and the individual grammars of each feature in
	this module, and meet all other conformance requirements of style sheets
	as described in this module. </p>
  <h3 class="heading settled" id="conform-responsible"><span class="content"> Requirements for Responsible Implementation of CSS</span><a class="self-link" href="#conform-responsible"></a></h3>
  <p>The following sections define several conformance requirements
		for implementing CSS responsibly,
		in a way that promotes interoperability in the present and future. </p>
  <h4 class="heading settled" id="conform-partial"><span class="content"> Partial Implementations</span><a class="self-link" href="#conform-partial"></a></h4>
  <p>So that authors can exploit the forward-compatible parsing rules to assign fallback values, <strong>CSS renderers <em>must</em> treat as invalid
		(and <a href="http://www.w3.org/TR/CSS2/conform.html#ignore">ignore as appropriate</a>)
		any at-rules, properties, property values, keywords, and other syntactic constructs
		for which they have no usable level of support</strong>.
		In particular, user agents <em>must not</em> selectively ignore
		unsupported property values and honor supported values in a single multi-value property declaration:
		if any value is considered invalid (as unsupported values must be),
		CSS requires that the entire declaration be ignored. </p>
  <h4 class="heading settled" id="conform-future-proofing"><span class="content"> Implementations of Unstable and Proprietary Features</span><a class="self-link" href="#conform-future-proofing"></a></h4>
  <p>To avoid clashes with future stable CSS features,
		the CSSWG recommends <a href="http://www.w3.org/TR/CSS/#future-proofing">following best practices</a> for the implementation of <a href="http://www.w3.org/TR/CSS/#unstable">unstable</a> features and <a href="http://www.w3.org/TR/CSS/#proprietary-extension">proprietary extensions</a> to CSS. </p>
  <h4 class="heading settled" id="conform-testing"><span class="content"> Implementations of CR-level Features</span><a class="self-link" href="#conform-testing"></a></h4>
  <p>Once a specification reaches the Candidate Recommendation stage,
		implementers should release an <a data-link-type="dfn" href="http://www.w3.org/TR/CSS/#vendor-prefix">unprefixed</a> implementation
		of any CR-level feature they can demonstrate
		to be correctly implemented according to spec,
		and should avoid exposing a prefixed variant of that feature. </p>
  <p>To establish and maintain the interoperability of CSS across
		implementations, the CSS Working Group requests that non-experimental
		CSS renderers submit an implementation report (and, if necessary, the
		testcases used for that implementation report) to the W3C before
		releasing an unprefixed implementation of any CSS features. Testcases
		submitted to W3C are subject to review and correction by the CSS
		Working Group. </p>
  <p>
   Further information on submitting testcases and implementation reports
		can be found from on the CSS Working Group’s website at <a href="http://www.w3.org/Style/CSS/Test/">http://www.w3.org/Style/CSS/Test/</a>.
		Questions should be directed to the <a href="http://lists.w3.org/Archives/Public/public-css-testsuite">public-css-testsuite@w3.org</a> mailing list. 
<script src="https://www.w3.org/scripts/TR/2016/fixup.js"></script>
  </p>
  <h2 class="no-num no-ref heading settled" id="index"><span class="content">Index</span><a class="self-link" href="#index"></a></h2>
  <h3 class="no-num no-ref heading settled" id="index-defined-here"><span class="content">Terms defined by this specification</span><a class="self-link" href="#index-defined-here"></a></h3>
  <ul class="index">
   <li><a href="#csstransition">CSSTransition</a><span>, in §4.1</span>
   <li><a href="#dom-csstransition-csstransition">CSSTransition(target, transitionProperty, transitionValue)</a><span>, in §4.1</span>
   <li><a href="#dom-csstransition-csstransition">CSSTransition(target, transitionProperty, transitionValue, options)</a><span>, in §4.1</span>
   <li><a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline">CSSTransition(target, transitionProperty, transitionValue, options, timeline)</a><span>, in §4.1</span>
   <li><a href="#current-transition-generation">current transition generation</a><span>, in §2</span>
   <li><a href="#elapsed-time">Elapsed time</a><span>, in §3.1</span>
   <li><a href="#expanded-transition-property-name">expanded transition property name</a><span>, in §2.1</span>
   <li><a href="#interval-end">interval end</a><span>, in §3.1</span>
   <li><a href="#interval-start">interval start</a><span>, in §3.1</span>
   <li><a href="#owning-element">owning element</a><span>, in §2.3</span>
   <li><a href="#transition-generation">transition generation</a><span>, in §2</span>
   <li><a href="#transition-phase">transition phase</a><span>, in §3.1</span>
   <li><a href="#dom-csstransition-transitionproperty">transitionProperty</a><span>, in §4.1</span>
  </ul>
  <aside class="dfn-panel" data-for="term-for-propdef-animation">
   <a href="https://drafts.csswg.org/css-animations-1/#propdef-animation">https://drafts.csswg.org/css-animations-1/#propdef-animation</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-animation">4.2. Requirements on pending style changes</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-propdef-border-left-width">
   <a href="https://drafts.csswg.org/css-backgrounds-3/#propdef-border-left-width">https://drafts.csswg.org/css-backgrounds-3/#propdef-border-left-width</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-border-left-width">2.1. The transition property name</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-computed-value">
   <a href="https://drafts.csswg.org/css-cascade-4/#computed-value">https://drafts.csswg.org/css-cascade-4/#computed-value</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-computed-value">4.2. Requirements on pending style changes</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-propdef-opacity">
   <a href="https://drafts.csswg.org/css-color-4/#propdef-opacity">https://drafts.csswg.org/css-color-4/#propdef-opacity</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-opacity">4.2. Requirements on pending style changes</a> <a href="#ref-for-propdef-opacity①">(2)</a> <a href="#ref-for-propdef-opacity②">(3)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-transitionevent">
   <a href="https://drafts.csswg.org/css-transitions-1/#transitionevent">https://drafts.csswg.org/css-transitions-1/#transitionevent</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-transitionevent">3.1. Event dispatch</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-valdef-transition-property-all">
   <a href="https://drafts.csswg.org/css-transitions-1/#valdef-transition-property-all">https://drafts.csswg.org/css-transitions-1/#valdef-transition-property-all</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-valdef-transition-property-all">2.1. The transition property name</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-Events-TransitionEvent-elapsedTime">
   <a href="https://drafts.csswg.org/css-transitions-1/#Events-TransitionEvent-elapsedTime">https://drafts.csswg.org/css-transitions-1/#Events-TransitionEvent-elapsedTime</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-Events-TransitionEvent-elapsedTime">3.1. Event dispatch</a> <a href="#ref-for-Events-TransitionEvent-elapsedTime①">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-style-change-event">
   <a href="https://drafts.csswg.org/css-transitions-1/#style-change-event">https://drafts.csswg.org/css-transitions-1/#style-change-event</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-style-change-event">2. Starting of transitions</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-propdef-transition-property">
   <a href="https://drafts.csswg.org/css-transitions-1/#propdef-transition-property">https://drafts.csswg.org/css-transitions-1/#propdef-transition-property</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-transition-property">2.1. The transition property name</a>
    <li><a href="#ref-for-propdef-transition-property①">2.3. Owning element</a>
    <li><a href="#ref-for-propdef-transition-property②">6. Issues deferred from previous levels of the spec</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-propdef-transition-timing-function">
   <a href="https://drafts.csswg.org/css-transitions-1/#propdef-transition-timing-function">https://drafts.csswg.org/css-transitions-1/#propdef-transition-timing-function</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-propdef-transition-timing-function">2.2. The transition timing function</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-transitioncancel">
   <a href="https://drafts.csswg.org/css-transitions-1/#transitioncancel">https://drafts.csswg.org/css-transitions-1/#transitioncancel</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-transitioncancel">3.1. Event dispatch</a> <a href="#ref-for-transitioncancel①">(2)</a> <a href="#ref-for-transitioncancel②">(3)</a> <a href="#ref-for-transitioncancel③">(4)</a> <a href="#ref-for-transitioncancel④">(5)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-transitionend">
   <a href="https://drafts.csswg.org/css-transitions-1/#transitionend">https://drafts.csswg.org/css-transitions-1/#transitionend</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-transitionend">3.1. Event dispatch</a> <a href="#ref-for-transitionend①">(2)</a> <a href="#ref-for-transitionend②">(3)</a> <a href="#ref-for-transitionend③">(4)</a> <a href="#ref-for-transitionend④">(5)</a> <a href="#ref-for-transitionend⑤">(6)</a> <a href="#ref-for-transitionend⑥">(7)</a> <a href="#ref-for-transitionend⑦">(8)</a> <a href="#ref-for-transitionend⑧">(9)</a> <a href="#ref-for-transitionend⑨">(10)</a> <a href="#ref-for-transitionend①⓪">(11)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-transitionrun">
   <a href="https://drafts.csswg.org/css-transitions-1/#transitionrun">https://drafts.csswg.org/css-transitions-1/#transitionrun</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-transitionrun">3.1. Event dispatch</a> <a href="#ref-for-transitionrun①">(2)</a> <a href="#ref-for-transitionrun②">(3)</a> <a href="#ref-for-transitionrun③">(4)</a> <a href="#ref-for-transitionrun④">(5)</a> <a href="#ref-for-transitionrun⑤">(6)</a> <a href="#ref-for-transitionrun⑥">(7)</a> <a href="#ref-for-transitionrun⑦">(8)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-transitionstart">
   <a href="https://drafts.csswg.org/css-transitions-1/#transitionstart">https://drafts.csswg.org/css-transitions-1/#transitionstart</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-transitionstart">3.1. Event dispatch</a> <a href="#ref-for-transitionstart①">(2)</a> <a href="#ref-for-transitionstart②">(3)</a> <a href="#ref-for-transitionstart③">(4)</a> <a href="#ref-for-transitionstart④">(5)</a> <a href="#ref-for-transitionstart⑤">(6)</a> <a href="#ref-for-transitionstart⑥">(7)</a> <a href="#ref-for-transitionstart⑦">(8)</a> <a href="#ref-for-transitionstart⑧">(9)</a> <a href="#ref-for-transitionstart⑨">(10)</a> <a href="#ref-for-transitionstart①⓪">(11)</a> <a href="#ref-for-transitionstart①①">(12)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-cssomstring">
   <a href="https://drafts.csswg.org/cssom-1/#cssomstring">https://drafts.csswg.org/cssom-1/#cssomstring</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-cssomstring">4.1. The CSSTransition interface</a> <a href="#ref-for-cssomstring①">(2)</a> <a href="#ref-for-cssomstring②">(3)</a> <a href="#ref-for-cssomstring③">(4)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-dom-window-getcomputedstyle">
   <a href="https://drafts.csswg.org/cssom-1/#dom-window-getcomputedstyle">https://drafts.csswg.org/cssom-1/#dom-window-getcomputedstyle</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-dom-window-getcomputedstyle">4.2. Requirements on pending style changes</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-concept-tree-order">
   <a href="https://dom.spec.whatwg.org/#concept-tree-order">https://dom.spec.whatwg.org/#concept-tree-order</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-concept-tree-order">2.4. Animation composite order</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-animatable">
   <a href="https://drafts.csswg.org/web-animations-1/#animatable">https://drafts.csswg.org/web-animations-1/#animatable</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-animatable">4.1. The CSSTransition interface</a> <a href="#ref-for-animatable①">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-animation">
   <a href="https://w3c.github.io/web-animations/#animation">https://w3c.github.io/web-animations/#animation</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-animation">2.4. Animation composite order</a>
    <li><a href="#ref-for-animation①">4.1. The CSSTransition interface</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-animationtimeline">
   <a href="https://drafts.csswg.org/web-animations-1/#animationtimeline">https://drafts.csswg.org/web-animations-1/#animationtimeline</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-animationtimeline">4.1. The CSSTransition interface</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-keyframeeffect">
   <a href="https://drafts.csswg.org/web-animations-1/#keyframeeffect">https://drafts.csswg.org/web-animations-1/#keyframeeffect</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-keyframeeffect">2.2. The transition timing function</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-dictdef-keyframeeffectoptions">
   <a href="https://drafts.csswg.org/web-animations-1/#dictdef-keyframeeffectoptions">https://drafts.csswg.org/web-animations-1/#dictdef-keyframeeffectoptions</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-dictdef-keyframeeffectoptions">4.1. The CSSTransition interface</a> <a href="#ref-for-dictdef-keyframeeffectoptions①">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-active-duration">
   <a href="https://w3c.github.io/web-animations/#active-duration">https://w3c.github.io/web-animations/#active-duration</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-active-duration">3.1. Event dispatch</a> <a href="#ref-for-active-duration①">(2)</a> <a href="#ref-for-active-duration②">(3)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-active-time">
   <a href="https://w3c.github.io/web-animations/#active-time">https://w3c.github.io/web-animations/#active-time</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-active-time">3.1. Event dispatch</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-animation">
   <a href="https://w3c.github.io/web-animations/#animation">https://w3c.github.io/web-animations/#animation</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-animation">2.4. Animation composite order</a>
    <li><a href="#ref-for-animation①">4.1. The CSSTransition interface</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-animation-class">
   <a href="https://w3c.github.io/web-animations/#animation-class">https://w3c.github.io/web-animations/#animation-class</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-animation-class">2.4. Animation composite order</a> <a href="#ref-for-animation-class①">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-current-iteration">
   <a href="https://w3c.github.io/web-animations/#current-iteration">https://w3c.github.io/web-animations/#current-iteration</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-current-iteration">3.1. Event dispatch</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-current-time">
   <a href="https://w3c.github.io/web-animations/#current-time">https://w3c.github.io/web-animations/#current-time</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-current-time">3.1. Event dispatch</a> <a href="#ref-for-current-time①">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-dom-effecttiming-easing">
   <a href="https://drafts.csswg.org/web-animations-1/#dom-effecttiming-easing">https://drafts.csswg.org/web-animations-1/#dom-effecttiming-easing</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-dom-effecttiming-easing">2.2. The transition timing function</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-fill-mode">
   <a href="https://w3c.github.io/web-animations/#fill-mode">https://w3c.github.io/web-animations/#fill-mode</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-fill-mode">3.1. Event dispatch</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-dom-animatable-getanimations">
   <a href="https://www.w3.org/TR/web-animations-1/#dom-animatable-getanimations">https://www.w3.org/TR/web-animations-1/#dom-animatable-getanimations</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-dom-animatable-getanimations">4.2. Requirements on pending style changes</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-dom-animationeffect-getcomputedtiming">
   <a href="https://drafts.csswg.org/web-animations-1/#dom-animationeffect-getcomputedtiming">https://drafts.csswg.org/web-animations-1/#dom-animationeffect-getcomputedtiming</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-dom-animationeffect-getcomputedtiming">2.2. The transition timing function</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-global-animation-list">
   <a href="https://w3c.github.io/web-animations/#global-animation-list">https://w3c.github.io/web-animations/#global-animation-list</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-global-animation-list">2.4. Animation composite order</a> <a href="#ref-for-global-animation-list①">(2)</a> <a href="#ref-for-global-animation-list②">(3)</a> <a href="#ref-for-global-animation-list③">(4)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-idle-play-state">
   <a href="https://w3c.github.io/web-animations/#idle-play-state">https://w3c.github.io/web-animations/#idle-play-state</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-idle-play-state">2.4. Animation composite order</a> <a href="#ref-for-idle-play-state①">(2)</a> <a href="#ref-for-idle-play-state②">(3)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-iteration-duration">
   <a href="https://w3c.github.io/web-animations/#iteration-duration">https://w3c.github.io/web-animations/#iteration-duration</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-iteration-duration">3.1. Event dispatch</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-iteration-start">
   <a href="https://w3c.github.io/web-animations/#iteration-start">https://w3c.github.io/web-animations/#iteration-start</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-iteration-start">3.1. Event dispatch</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-pending-play-state">
   <a href="https://w3c.github.io/web-animations/#pending-play-state">https://w3c.github.io/web-animations/#pending-play-state</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-pending-play-state">3.1. Event dispatch</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-sampling">
   <a href="https://w3c.github.io/web-animations/#sampling">https://w3c.github.io/web-animations/#sampling</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-sampling">3.1. Event dispatch</a> <a href="#ref-for-sampling①">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-start-delay">
   <a href="https://w3c.github.io/web-animations/#start-delay">https://w3c.github.io/web-animations/#start-delay</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-start-delay">3.1. Event dispatch</a> <a href="#ref-for-start-delay①">(2)</a> <a href="#ref-for-start-delay②">(3)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-target-effect">
   <a href="https://w3c.github.io/web-animations/#target-effect">https://w3c.github.io/web-animations/#target-effect</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-target-effect">3.1. Event dispatch</a> <a href="#ref-for-target-effect①">(2)</a> <a href="#ref-for-target-effect②">(3)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-target-effect-end">
   <a href="https://w3c.github.io/web-animations/#target-effect-end">https://w3c.github.io/web-animations/#target-effect-end</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-target-effect-end">3.1. Event dispatch</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-unresolved">
   <a href="https://w3c.github.io/web-animations/#unresolved">https://w3c.github.io/web-animations/#unresolved</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-unresolved">3.1. Event dispatch</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-Exposed">
   <a href="https://heycam.github.io/webidl/#Exposed">https://heycam.github.io/webidl/#Exposed</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-Exposed">4.1. The CSSTransition interface</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="term-for-idl-unrestricted-double">
   <a href="https://heycam.github.io/webidl/#idl-unrestricted-double">https://heycam.github.io/webidl/#idl-unrestricted-double</a><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-idl-unrestricted-double">4.1. The CSSTransition interface</a> <a href="#ref-for-idl-unrestricted-double①">(2)</a>
   </ul>
  </aside>
  <h3 class="no-num no-ref heading settled" id="index-defined-elsewhere"><span class="content">Terms defined by reference</span><a class="self-link" href="#index-defined-elsewhere"></a></h3>
  <ul class="index">
   <li>
    <a data-link-type="biblio">[css-animations-1]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-propdef-animation" style="color:initial">animation</span>
    </ul>
   <li>
    <a data-link-type="biblio">[css-backgrounds-3]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-propdef-border-left-width" style="color:initial">border-left-width</span>
    </ul>
   <li>
    <a data-link-type="biblio">[css-cascade-4]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-computed-value" style="color:initial">computed value</span>
    </ul>
   <li>
    <a data-link-type="biblio">[css-color-4]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-propdef-opacity" style="color:initial">opacity</span>
    </ul>
   <li>
    <a data-link-type="biblio">[CSS3-TRANSITIONS]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-transitionevent" style="color:initial">TransitionEvent</span>
     <li><span class="dfn-paneled" id="term-for-valdef-transition-property-all" style="color:initial">all</span>
     <li><span class="dfn-paneled" id="term-for-Events-TransitionEvent-elapsedTime" style="color:initial">elapsedTime</span>
     <li><span class="dfn-paneled" id="term-for-style-change-event" style="color:initial">style change event</span>
     <li><span class="dfn-paneled" id="term-for-propdef-transition-property" style="color:initial">transition-property</span>
     <li><span class="dfn-paneled" id="term-for-propdef-transition-timing-function" style="color:initial">transition-timing-function</span>
     <li><span class="dfn-paneled" id="term-for-transitioncancel" style="color:initial">transitioncancel</span>
     <li><span class="dfn-paneled" id="term-for-transitionend" style="color:initial">transitionend</span>
     <li><span class="dfn-paneled" id="term-for-transitionrun" style="color:initial">transitionrun</span>
     <li><span class="dfn-paneled" id="term-for-transitionstart" style="color:initial">transitionstart</span>
    </ul>
   <li>
    <a data-link-type="biblio">[cssom-1]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-cssomstring" style="color:initial">CSSOMString</span>
     <li><span class="dfn-paneled" id="term-for-dom-window-getcomputedstyle" style="color:initial">getComputedStyle(elt)</span>
    </ul>
   <li>
    <a data-link-type="biblio">[DOM]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-concept-tree-order" style="color:initial">tree order</span>
    </ul>
   <li>
    <a data-link-type="biblio">[WEB-ANIMATIONS]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-animatable" style="color:initial">Animatable</span>
     <li><span class="dfn-paneled" id="term-for-animation" style="color:initial">Animation</span>
     <li><span class="dfn-paneled" id="term-for-animationtimeline" style="color:initial">AnimationTimeline</span>
     <li><span class="dfn-paneled" id="term-for-keyframeeffect" style="color:initial">KeyframeEffect</span>
     <li><span class="dfn-paneled" id="term-for-dictdef-keyframeeffectoptions" style="color:initial">KeyframeEffectOptions</span>
     <li><span class="dfn-paneled" id="term-for-active-duration" style="color:initial">active duration</span>
     <li><span class="dfn-paneled" id="term-for-active-time" style="color:initial">active time</span>
     <li><span class="dfn-paneled" id="term-for-animation①" style="color:initial">animation</span>
     <li><span class="dfn-paneled" id="term-for-animation-class" style="color:initial">animation class</span>
     <li><span class="dfn-paneled" id="term-for-current-iteration" style="color:initial">current iteration</span>
     <li><span class="dfn-paneled" id="term-for-current-time" style="color:initial">current time</span>
     <li><span class="dfn-paneled" id="term-for-dom-effecttiming-easing" style="color:initial">easing</span>
     <li><span class="dfn-paneled" id="term-for-fill-mode" style="color:initial">fill mode</span>
     <li><span class="dfn-paneled" id="term-for-dom-animatable-getanimations" style="color:initial">getAnimations()</span>
     <li><span class="dfn-paneled" id="term-for-dom-animationeffect-getcomputedtiming" style="color:initial">getComputedTiming()</span>
     <li><span class="dfn-paneled" id="term-for-global-animation-list" style="color:initial">global animation list</span>
     <li><span class="dfn-paneled" id="term-for-idle-play-state" style="color:initial">idle play state</span>
     <li><span class="dfn-paneled" id="term-for-iteration-duration" style="color:initial">iteration duration</span>
     <li><span class="dfn-paneled" id="term-for-iteration-start" style="color:initial">iteration start</span>
     <li><span class="dfn-paneled" id="term-for-pending-play-state" style="color:initial">pending play state</span>
     <li><span class="dfn-paneled" id="term-for-sampling" style="color:initial">sampling</span>
     <li><span class="dfn-paneled" id="term-for-start-delay" style="color:initial">start delay</span>
     <li><span class="dfn-paneled" id="term-for-target-effect" style="color:initial">target effect</span>
     <li><span class="dfn-paneled" id="term-for-target-effect-end" style="color:initial">target effect end</span>
     <li><span class="dfn-paneled" id="term-for-unresolved" style="color:initial">unresolved</span>
    </ul>
   <li>
    <a data-link-type="biblio">[WebIDL]</a> defines the following terms:
    <ul>
     <li><span class="dfn-paneled" id="term-for-Exposed" style="color:initial">Exposed</span>
     <li><span class="dfn-paneled" id="term-for-idl-unrestricted-double" style="color:initial">unrestricted double</span>
    </ul>
  </ul>
  <h2 class="no-num no-ref heading settled" id="references"><span class="content">References</span><a class="self-link" href="#references"></a></h2>
  <h3 class="no-num no-ref heading settled" id="normative"><span class="content">Normative References</span><a class="self-link" href="#normative"></a></h3>
  <dl>
   <dt id="biblio-css-backgrounds-3">[CSS-BACKGROUNDS-3]
   <dd>Bert Bos; Elika Etemad; Brad Kemper. <a href="https://www.w3.org/TR/css-backgrounds-3/">CSS Backgrounds and Borders Module Level 3</a>. 17 October 2017. CR. URL: <a href="https://www.w3.org/TR/css-backgrounds-3/">https://www.w3.org/TR/css-backgrounds-3/</a>
   <dt id="biblio-css-cascade-4">[CSS-CASCADE-4]
   <dd>Elika Etemad; Tab Atkins Jr.. <a href="https://www.w3.org/TR/css-cascade-4/">CSS Cascading and Inheritance Level 4</a>. 28 August 2018. CR. URL: <a href="https://www.w3.org/TR/css-cascade-4/">https://www.w3.org/TR/css-cascade-4/</a>
   <dt id="biblio-css3-transitions">[CSS3-TRANSITIONS]
   <dd>David Baron; et al. <a href="https://www.w3.org/TR/css-transitions-1/">CSS Transitions</a>. 11 October 2018. WD. URL: <a href="https://www.w3.org/TR/css-transitions-1/">https://www.w3.org/TR/css-transitions-1/</a>
   <dt id="biblio-cssom-1">[CSSOM-1]
   <dd>Simon Pieters; Glenn Adams. <a href="https://www.w3.org/TR/cssom-1/">CSS Object Model (CSSOM)</a>. 17 March 2016. WD. URL: <a href="https://www.w3.org/TR/cssom-1/">https://www.w3.org/TR/cssom-1/</a>
   <dt id="biblio-dom">[DOM]
   <dd>Anne van Kesteren. <a href="https://dom.spec.whatwg.org/">DOM Standard</a>. Living Standard. URL: <a href="https://dom.spec.whatwg.org/">https://dom.spec.whatwg.org/</a>
   <dt id="biblio-rfc2119">[RFC2119]
   <dd>S. Bradner. <a href="https://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>. March 1997. Best Current Practice. URL: <a href="https://tools.ietf.org/html/rfc2119">https://tools.ietf.org/html/rfc2119</a>
   <dt id="biblio-web-animations">[WEB-ANIMATIONS]
   <dd>Brian Birtles; et al. <a href="https://www.w3.org/TR/web-animations-1/">Web Animations</a>. 11 October 2018. WD. URL: <a href="https://www.w3.org/TR/web-animations-1/">https://www.w3.org/TR/web-animations-1/</a>
   <dt id="biblio-webidl">[WebIDL]
   <dd>Boris Zbarsky. <a href="https://heycam.github.io/webidl/">Web IDL</a>. 15 December 2016. ED. URL: <a href="https://heycam.github.io/webidl/">https://heycam.github.io/webidl/</a>
  </dl>
  <h3 class="no-num no-ref heading settled" id="informative"><span class="content">Informative References</span><a class="self-link" href="#informative"></a></h3>
  <dl>
   <dt id="biblio-css-animations-1">[CSS-ANIMATIONS-1]
   <dd>Dean Jackson; et al. <a href="https://www.w3.org/TR/css-animations-1/">CSS Animations Level 1</a>. 11 October 2018. WD. URL: <a href="https://www.w3.org/TR/css-animations-1/">https://www.w3.org/TR/css-animations-1/</a>
   <dt id="biblio-css-color-4">[CSS-COLOR-4]
   <dd>Tab Atkins Jr.; Chris Lilley. <a href="https://www.w3.org/TR/css-color-4/">CSS Color Module Level 4</a>. 5 March 2019. WD. URL: <a href="https://www.w3.org/TR/css-color-4/">https://www.w3.org/TR/css-color-4/</a>
  </dl>
  <h2 class="no-num no-ref heading settled" id="idl-index"><span class="content">IDL Index</span><a class="self-link" href="#idl-index"></a></h2>
<pre class="idl highlight def">[<a class="idl-code" data-link-type="extended-attribute" href="https://heycam.github.io/webidl/#Exposed" id="ref-for-Exposed①"><c- g>Exposed</c-></a>=<c- n>Window</c->]
<c- b>interface</c-> <a href="#csstransition"><code><c- g>CSSTransition</c-></code></a> : <a class="n" data-link-type="idl-name" href="https://w3c.github.io/web-animations/#animation" id="ref-for-animation①①"><c- n>Animation</c-></a> {
  <c- b>readonly</c-> <c- b>attribute</c-> <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/cssom-1/#cssomstring" id="ref-for-cssomstring④"><c- n>CSSOMString</c-></a> <a class="idl-code" data-link-type="attribute" data-readonly data-type="CSSOMString" href="#dom-csstransition-transitionproperty" id="ref-for-dom-csstransition-transitionproperty①"><c- g>transitionProperty</c-></a>;
};

[<a href="#dom-csstransition-csstransition"><code><c- g>Constructor</c-></code></a> (<a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/web-animations-1/#animatable" id="ref-for-animatable②"><c- n>Animatable</c-></a>? <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-target"><code><c- g>target</c-></code></a>,
              <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/cssom-1/#cssomstring" id="ref-for-cssomstring②①"><c- n>CSSOMString</c-></a> <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-transitionproperty"><code><c- g>transitionProperty</c-></code></a>,
              <c- b>any</c-> <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-transitionvalue"><code><c- g>transitionValue</c-></code></a>,
              <c- b>optional</c-> (<a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-unrestricted-double" id="ref-for-idl-unrestricted-double②"><c- b>unrestricted</c-> <c- b>double</c-></a> <c- b>or</c-> <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/web-animations-1/#dictdef-keyframeeffectoptions" id="ref-for-dictdef-keyframeeffectoptions②"><c- n>KeyframeEffectOptions</c-></a>) <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-options"><code><c- g>options</c-></code></a>),
 <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline"><code><c- g>Constructor</c-></code></a> (<a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/web-animations-1/#animatable" id="ref-for-animatable①①"><c- n>Animatable</c-></a>? <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-target"><code><c- g>target</c-></code></a>,
              <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/cssom-1/#cssomstring" id="ref-for-cssomstring③①"><c- n>CSSOMString</c-></a> <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-transitionproperty"><code><c- g>transitionProperty</c-></code></a>,
              <c- b>any</c-> <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-transitionvalue"><code><c- g>transitionValue</c-></code></a>,
              (<a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-unrestricted-double" id="ref-for-idl-unrestricted-double①①"><c- b>unrestricted</c-> <c- b>double</c-></a> <c- b>or</c-> <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/web-animations-1/#dictdef-keyframeeffectoptions" id="ref-for-dictdef-keyframeeffectoptions①①"><c- n>KeyframeEffectOptions</c-></a>) <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-options"><code><c- g>options</c-></code></a>,
              <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/web-animations-1/#animationtimeline" id="ref-for-animationtimeline①"><c- n>AnimationTimeline</c-></a>? <a href="#dom-csstransition-csstransition-target-transitionproperty-transitionvalue-options-timeline-timeline"><code><c- g>timeline</c-></code></a>)]
<c- b>partial</c-> <c- b>interface</c-> <a class="idl-code" data-link-type="interface" href="#csstransition" id="ref-for-csstransition③①"><c- g>CSSTransition</c-></a> { };

</pre>
  <h2 class="no-num no-ref heading settled" id="issues-index"><span class="content">Issues Index</span><a class="self-link" href="#issues-index"></a></h2>
  <div style="counter-reset:issue">
   <div class="issue"> Define the above more precisely once we rewrite firing of transitions
in terms of Web Animations concepts (specifically when we spell out when we
cancel an animation).<a href="#issue-e8892835"> ↵ </a></div>
   <div class="issue">
    <p>This interface needs a constructor. Perhaps something like the following,</p>
<pre class="idl highlight def">[<span><code><c- g>Constructor</c-></code></span> (<a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/web-animations-1/#animatable"><c- n>Animatable</c-></a>? <span><code><c- g>target</c-></code></span>,
              <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/cssom-1/#cssomstring"><c- n>CSSOMString</c-></a> <span><code><c- g>transitionProperty</c-></code></span>,
              <c- b>any</c-> <span><code><c- g>transitionValue</c-></code></span>,
              <c- b>optional</c-> (<a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-unrestricted-double"><c- b>unrestricted</c-> <c- b>double</c-></a> <c- b>or</c-> <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/web-animations-1/#dictdef-keyframeeffectoptions"><c- n>KeyframeEffectOptions</c-></a>) <span><code><c- g>options</c-></code></span>),
 <span><code><c- g>Constructor</c-></code></span> (<a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/web-animations-1/#animatable"><c- n>Animatable</c-></a>? <span><code><c- g>target</c-></code></span>,
              <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/cssom-1/#cssomstring"><c- n>CSSOMString</c-></a> <span><code><c- g>transitionProperty</c-></code></span>,
              <c- b>any</c-> <span><code><c- g>transitionValue</c-></code></span>,
              (<a class="idl-code" data-link-type="interface" href="https://heycam.github.io/webidl/#idl-unrestricted-double"><c- b>unrestricted</c-> <c- b>double</c-></a> <c- b>or</c-> <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/web-animations-1/#dictdef-keyframeeffectoptions"><c- n>KeyframeEffectOptions</c-></a>) <span><code><c- g>options</c-></code></span>,
              <a class="n" data-link-type="idl-name" href="https://drafts.csswg.org/web-animations-1/#animationtimeline"><c- n>AnimationTimeline</c-></a>? <span><code><c- g>timeline</c-></code></span>)]
<c- b>partial</c-> <c- b>interface</c-> <a class="idl-code" data-link-type="interface" href="#csstransition"><c- g>CSSTransition</c-></a> { };
</pre>
    <p>Using <code>any</code> as the type for <code>transitionValue</code> would allow
the following usage:</p>
<pre class="example lang-javascript highlight"><c- a>var</c-> transition <c- o>=</c-> <c- k>new</c-> CSSTransition<c- p>(</c->elem<c- p>,</c-> <c- t>'opacity'</c-><c- p>,</c-> <c- mi>1</c-><c- p>,</c-> <c- mi>2000</c-><c- p>);</c->
transition<c- p>.</c->play<c- p>();</c->
</pre>
    <p>The above example, however, is <em>not</em> equivalent to triggering a
transition. It has the following differences:</p>
    <ul>
     <li data-md>
      <p>It does not update the specified style.</p>
     <li data-md>
      <p>It would not cancel any existing transition on the given property unless
we add special wording to that effect.</p>
     <li data-md>
      <p>It would exhibit different composite order to a regular transition
(this should be easily fixed, however).</p>
     <li data-md>
      <p>It has been suggested that <a href="https://github.com/w3c/web-animations/issues/62#issuecomment-117357703">script-generated
animations should not apply to the transition level of the cascade</a>.</p>
    </ul>
    <p>It is unclear how much we should extend the <code class="idl"><a data-link-type="idl" href="#csstransition">CSSTransition</a></code> constructor to
overcome the above limitations so that it can be used to generate transitions
programmatically, or whether we should introduce a separate helper method such
as has been <a href="https://lists.w3.org/Archives/Public/www-style/2011Mar/0729.html">suggested
elsewhere</a>.</p>
     <a href="#issue-25ee9f1c"> ↵ </a>
   </div>
   <div class="issue">
    <p> More powerful timing function syntax
			is a common request from developers.
			See, for example: <a href="https://lists.w3.org/Archives/Public/www-style/2013Jun/0376.html">2013 message</a> or <a href="https://lists.w3.org/Archives/Public/public-fx/2015JulSep/thread.html#msg34">2015 thread</a>. </p>
     <a href="#issue-af4a1d54"> ↵ </a>
   </div>
   <div class="issue">
    <p> Developers frequently have to trigger style flushes
			in order to force transitions to start.
			It would be good to have an API
			that would avoid this requirement.
			See, for example, <a href="https://lists.w3.org/Archives/Public/www-style/2011Mar/0729.html">2011 proposal</a>. </p>
     <a href="#issue-b197fc50"> ↵ </a>
   </div>
   <div class="issue"> We may ultimately want to support a keypath syntax
		for the <a class="property" data-link-type="propdesc" href="https://drafts.csswg.org/css-transitions-1/#propdef-transition-property">transition-property</a> property.
		A keypath syntax
		would enable different transitions
		to be specified
		for components of a property.
		For example
		the blur of a shadow
		could have
		a different transition
		than the color of a shadow. <a href="#issue-5a3a5638"> ↵ </a></div>
  </div>
  <aside class="dfn-panel" data-for="current-transition-generation">
   <b><a href="#current-transition-generation">#current-transition-generation</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-current-transition-generation">2. Starting of transitions</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="transition-generation">
   <b><a href="#transition-generation">#transition-generation</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-transition-generation">2.4. Animation composite order</a> <a href="#ref-for-transition-generation①">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="expanded-transition-property-name">
   <b><a href="#expanded-transition-property-name">#expanded-transition-property-name</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-expanded-transition-property-name">2.4. Animation composite order</a>
    <li><a href="#ref-for-expanded-transition-property-name①">4.1. The CSSTransition interface</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="owning-element">
   <b><a href="#owning-element">#owning-element</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-owning-element">2.3. Owning element</a> <a href="#ref-for-owning-element①">(2)</a> <a href="#ref-for-owning-element②">(3)</a>
    <li><a href="#ref-for-owning-element③">2.4. Animation composite order</a> <a href="#ref-for-owning-element④">(2)</a> <a href="#ref-for-owning-element⑤">(3)</a> <a href="#ref-for-owning-element⑥">(4)</a> <a href="#ref-for-owning-element⑦">(5)</a> <a href="#ref-for-owning-element⑧">(6)</a> <a href="#ref-for-owning-element⑨">(7)</a> <a href="#ref-for-owning-element①⓪">(8)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="transition-phase">
   <b><a href="#transition-phase">#transition-phase</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-transition-phase">3.1. Event dispatch</a> <a href="#ref-for-transition-phase①">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="interval-start">
   <b><a href="#interval-start">#interval-start</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-interval-start">3.1. Event dispatch</a> <a href="#ref-for-interval-start①">(2)</a> <a href="#ref-for-interval-start②">(3)</a> <a href="#ref-for-interval-start③">(4)</a> <a href="#ref-for-interval-start④">(5)</a> <a href="#ref-for-interval-start⑤">(6)</a> <a href="#ref-for-interval-start⑥">(7)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="interval-end">
   <b><a href="#interval-end">#interval-end</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-interval-end">3.1. Event dispatch</a> <a href="#ref-for-interval-end①">(2)</a> <a href="#ref-for-interval-end②">(3)</a> <a href="#ref-for-interval-end③">(4)</a> <a href="#ref-for-interval-end④">(5)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="elapsed-time">
   <b><a href="#elapsed-time">#elapsed-time</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-elapsed-time">3.1. Event dispatch</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="csstransition">
   <b><a href="#csstransition">#csstransition</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-csstransition">2.3. Owning element</a>
    <li><a href="#ref-for-csstransition①">2.4. Animation composite order</a> <a href="#ref-for-csstransition②">(2)</a>
    <li><a href="#ref-for-csstransition③">4.1. The CSSTransition interface</a> <a href="#ref-for-csstransition④">(2)</a>
    <li><a href="#ref-for-csstransition⑤">4.2. Requirements on pending style changes</a> <a href="#ref-for-csstransition⑥">(2)</a>
   </ul>
  </aside>
  <aside class="dfn-panel" data-for="dom-csstransition-transitionproperty">
   <b><a href="#dom-csstransition-transitionproperty">#dom-csstransition-transitionproperty</a></b><b>Referenced in:</b>
   <ul>
    <li><a href="#ref-for-dom-csstransition-transitionproperty">4.1. The CSSTransition interface</a>
   </ul>
  </aside>
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